Curable epoxy resins have been used for many years as components in coating compositions. However, the properties of coatings produced using aqueous epoxy resin dispersions have long been considered inferior to those of coating in which the resin is used in the form of a solution in an organic solvent. This was mainly attributed to the fact that the emulsifiers used, for example nonylphenol ethoxylates, migrate to the surface of the film where they adversely affect its properties. One way of solving this problem is to use so-called reactive emulsifiers which, where the epoxy resin is crosslinked with a diamine or polyamide or other hardener, react with the hardener and thus become part of the coating. Aqueous dispersions of special reactive emulsifiers are known from the prior art.
EP-A-605 and U.S. Pat. No. 4,197,389 describe a hardener in the form of a reaction product of a) at least one polyepoxy compound, b) at least one polyalkylene polyether polyol and c) at least one polyamine.
EP-A-387 418, EP-A-714 924 and U.S. Pat. No. 5,489,630 describe hardeners for epoxy resins which are obtained by reacting polyalkylene polyether amines with di- and/or polyepoxy compounds to form an intermediate product and reacting the intermediate product obtained with a primary or secondary amine.
EP-A-717 059 describes hardeners for epoxy resins which are obtained by reacting a polyalkylene oxide polyether monoalcohol with a polyepoxide to form an intermediate product and reacting the intermediate product obtained with a polyamine.
EP-A-717 063 describes hardeners for epoxy resins which are obtained by reacting a polyalkylene oxide monoamine with di- and/or polycarboxylic acids to form an intermediate product and reacting the intermediate product obtained with a diamine or polyamine.
EP-A-709 418 describes a hardener for epoxy resins which is obtained by reaction of (A) a polyamine, (B) an alkoxy polyethylene polyether compound containing epoxy groups and (C) a hydrophobic epoxy compound.
The present invention relates generally to hardeners for epoxy resins, the hardeners based on xcex1,xcex2-unsaturated carboxylic acid esters, processes for their production, aqueous dispersions containing such hardeners, and to their use in coating solid substrates.
The problem addressed by the present invention was to provide hardeners for curable epoxy resins which, unless they were soluble in water, on the one hand would be self-dispersible in water, but which in addition would also be suitable as dispersants for curable epoxy resins in aqueous media.
The expression xe2x80x9cself-dispersiblexe2x80x9d in the context of the present invention means that the hardeners can be dispersed or emulsified spontaneously in aqueous media without the use of additional additives, such as emulsifying or dispersing additives. In other words, the hardeners to be developed are those which would be capable of self-dispersion and/or self-emulsification in aqueous media. In the interests of simplicity, the term xe2x80x9cself-dispersingxe2x80x9d is used for this property throughout the present specification.
The hardeners to be developed would be above all so-called reactive hardeners, i.e. over and above the properties mentioned, namely self-dispersibility in water and, in addition, suitability as dispersants for curable epoxy resins in aqueous media, would be capable of reacting with curable epoxy resins, i.e. of being hardeners for curable epoxy resins.
Another problem addressed by the invention was to provide aqueous dispersions of self-dispersible hardeners which would be distinguished by high stability in storage under practical storage conditions.
Another problem addressed by the invention was to provide coating compositions containing a self-dispersible hardener, the coating obtained from the coating composition after the hardening process being distinguished by excellent properties.
It has now surprisingly been found that hardeners obtainable by reaction of xcex1,xcex2-unsaturated carboxylic acid esters with mono-, di- or polyaminopolyalkylene oxide compound, subsequent reaction of the intermediate product obtained with an aromatic polyhydroxy compound, further reaction with an epoxy resin known from the prior art and, finally, reaction with one or more primary and/or secondary amines excellently satisfy the requirements mentioned in every respect.
The present invention relates first to hardeners for curable epoxy resins obtainable by
(a) reacting one or more xcex1,xcex2-unsaturated carboxylic acid esters (I)
R2R3Cxe2x95x90C(R4)COOR1xe2x80x83xe2x80x83(I)
where R1 is an aromatic or aliphatic radical containing up to 15 carbon atoms, the substituents R2, R3 and R4 independently of one another represent hydrogen, branched or unbranched, aliphatic or aromatic groups containing up to 20 carbon atoms or a group xe2x80x94(CH2)nxe2x80x94COOR1, where R1 is as defined above and n is a number of 0 to 10, with
(b) one or more mono-, di- or polyaminopolyalkylene oxide compounds, compounds (a) and (b) being used in such quantities that the equivalent ratio of the reactive hydrogen atoms at the aminonitrogen atoms of (b) to the Cxe2x95x90C double bond in the xcex1,xcex2-position to the group COOR1 shown in formula (I) in the carboxylic acid esters (a) is in the range from 10:1 to 1: 10,
subsequently reacting the intermediate product Z1 obtained with
(c) one or more polyhydroxy compounds, the equivalent ratio of ester groups in the intermediate compound Z1 to hydroxy groups in the polyhydroxy compound (c) being adjusted to a value of 1:1.1 to 1-10,
and subsequently reacting the intermediate product Z2 obtained with
(d) one or more polyepoxides, the equivalent ratio of oxirane rings in polyepoxide (d) to hydroxyl groups in the intermediate product Z2 being adjusted to a value of 1.5:1 to 6:1,
and subsequently reacting the intermediate product Z3 obtained with
(e) one or more primary and/or secondary amines, the equivalent ratio of oxirane rings in the intermediate product Z3 to the reactive H atoms at the aminonitrogen atoms of (e) being adjusted to a value of 1:1.5 to 1:20.
The hardeners according to the invention are either liquid or solid substances, depending on their molecular weight.
The present invention also includes processes for the production of hardeners for curable epoxy resins.
The expression xe2x80x9cequivalent ratioxe2x80x9d is familiar to the expert. The basic concept behind the notion of the equivalent is that, for every substance participating in a reaction, the reactive groups involved in the desired reaction are taken into consideration. By indicating an equivalent ratio, it is possible to express the ratio which all the various reactive groups of the compounds (x) and (y) used bear to one another. It is important in this connection to bear in mind that a reactive group is understood to be the smallest possible reactive group, i.e. the notion of the reactive group is not identical with the notion of the functional group. In the case of H-acid compounds, this means for example that, although OH groups or NH groups represent such reactive groups, NH2 groups with two reactive H atoms positioned at the same nitrogen atom do not. In their case, the two hydrogen atoms within the functional group NH2 are appropriately regarded as reactive groups so that the functional group NH2 contains two reactive groups, namely the hydrogen atoms. Example: if a compound (a) containing one olefinic double bond in the xcex1,xcex2-position to a carboxyl group per molecule is reacted with a compound (b) containing one NH2 group per molecule by a Michael addition, compound (a) is regarded as containing one reactive group Cxe2x95x90C per molecule whereas compound (b) is regarded as containing two reactive hydrogen atoms attached to the nitrogen. If, now, (a) and (b) were to be reacted in an equivalent ratio of 1:1, one mole of (a) would have to be reacted with half a mole of (b) because (b) does of course contain two reactive groups per molecule. By contrast, for an equivalent ratio of (a) to (b) of 1:2, 1 mole of (a) would have to be reacted with 1 mole of (b). An equivalent ratio of, for example, (a) to (b) of 1:10 could of course also be adjusted although in that case 1 mole of (a) would have to be reacted with 5 moles of (b). This would mean that component (b) would be used in excess because, of course, at most 1 mole of component (b) could theoretically be reacted with (a) in a Michael addition.
In one embodiment, compounds (a) and (b) are used in such quantities that the equivalent ratio of reactive hydrogen atoms at the aminonitrogen atoms of (b) to the Cxe2x95x90C double bond in the xcex1,xcex2-position to the group COOR1 in formula (I) in the carboxylic acid esters (a) is in the range from 4:1 to 1:4 and more particularly in the range from 2.5:1 to 1.5:1.
In another embodiment, the equivalent ratio of ester groups in the intermediate compound Z1 to hydroxy groups in the polyhydroxy compound (c) is adjusted to a value of 1:1.4 to 1:3.
In another embodiment, the equivalent ratio of oxirane rings in the polyepoxide (d) to hydroxyl groups in the intermediate product Z2 is adjusted to a value in the range from 2.5:1 to 3.5:1.
Examples of xcex1,xcex2-unsaturated carboxylic acid esters (a) corresponding to formula (I) to be used in accordance with the invention are methyl acrylate, ethyl acrylate, dimethyl maleate, diethyl maleate, dimethyl fumarate, diethyl fumarate, dimethyl itaconate, diethyl itaconate. Particularly preferred compounds (a) are dialkyl maleates, more particularly diethyl maleate and dimethyl maleate.
Suitable amino components (b) are mono-, di- or polyaminopolyalkylene oxide compounds. By this is meant that these compounds contain on the one hand one, two or more amino functions (NH or NH2 functions) and, on the other hand, alkylene oxide units. The alkylene oxide units are, in particular, ethylene oxide, propylene oxide and butylene oxide, ethylene oxide and propylene oxide being particularly preferred. The compounds (b) are substances at least partly soluble in water at 20xc2x0 C.
The production of the compounds (b) is known from the prior art and comprises the reaction of hydroxyfunctional compounds with alkylene oxides and subsequent conversion of the resulting terminal hydroxyl groups into amino groups.
So far as the reaction of hydroxyfunctional compounds with alkylene oxides is concerned, ethoxylation and propoxylation are of particular importance. The following procedure is usually adopted: in a first step, the required hydroxyfunctional compounds are contacted with ethylene oxide and/or propylene oxide and the resulting mixture is reacted in the presence of an alkaline catalyst at temperatures in the range from 20 to 200xc2x0 C. Addition products of ethylene oxide (EO) and/or propylene oxide (PO) are obtained in this way. The addition products are preferably EO adducts or PO adducts or EO/PO adducts with the particular hydroxyfunctional compound. In the case of the EO/PO adducts, the addition of EO and PO may be carried out statistically or blockwise.
In one embodiment, substances with the general formula R8xe2x80x94Oxe2x80x94R9xe2x80x94CH2CH(R10)xe2x80x94NH2 are used as the compounds (b). In this formula:
R8 is a monofunctional organic group containing 1 to 12 carbon atoms which may be aliphatic, cycloaliphatic or aromatic,
R9 is a polyoxyalkylene group made up of 5 to 200 polyoxyalkylene units, more particularly EO and/or PO units,
R10 is hydrogen or an aliphatic radical containing up to 4 carbon atoms.
In the context of the present invention, particularly suitable representatives of the compounds (b) are the xe2x80x9cJeffaminesxe2x80x9d known to the expert which are commercially available substances. One example is xe2x80x9cJeffamine 2070xe2x80x9d which, according to the manufacturer Texaco, is produced by reacting methanol with ethylene oxide and propylene oxide and then converting the terminal hydroxyl groups of the intermediate product initially obtained into amine groups (cf. WO 96/20971, page 10, lines 12-15).
The compounds (b) preferably have average molecular weights (number average Mn) of 148 to 5,000 and more particularly in the range from 400 to 2,000.
The polyhydroxy compounds (c) may be aliphatic or aromatic.
In one embodiment, the polyols (c) are selected from the class of special aliphatic diols, namely the alkanediols, polyether diols and polyesterdiols.
The alkanediols are compounds corresponding to the general formula HOCH2xe2x80x94R5xe2x80x94CH2OH, where R5 is a hydrophobic hydrocarbon radical which may be saturated or unsaturated, linear or branched and may also contain aromatic structural elements. Examples are hexane-1,6-diol, heptane-1,7-diol and octane-1,8-diol, polyoxytetramethylenediolsxe2x80x94also known as polytetrahydrofuransxe2x80x94and the so-called dimerdiols.
Dimerdiols are well-known commercially available compounds which are obtained, for example, by reduction of dimer fatty acid esters. The dimer fatty acids on which these dimer fatty acid esters are based are carboxylic acids which may be obtained by oligomerization of unsaturated carboxylic acids, generally fatty acids, such as oleic acid, linoleic acid, erucic acid and the like. The oligomerization is normally carried out at elevated temperature in the presence of a catalyst, for example of alumina. The substances obtainedxe2x80x94dimer fatty acid of technical qualityxe2x80x94are mixtures in which the dimerization products predominate. However, small amounts of higher oligomers, more particularly the trimer fatty acids, are also present. Dimer fatty acids are commercially available products and are marketed in various compositions and qualities. Abundant literature is available on the subject of dimer fatty acids, cf. for example the following articles: Fette and xc3x96le 26 (1994), pages 47-51; Speciality Chemicals 1984 (May Number), pages 17,18,22-24. Dimerdiols are well-known among experts, cf. for example a more recent article in which inter alia the production, structure and chemistry of the dimerdiols are discussed: Fat Sci. Technol. 95 (1993), No. 3, pages 91-94. According to the invention, preferred dimerdiols are those which have a dimer content of at least 50% and more particularly 75% and in which the number of carbon atoms per dimer molecule is mainly in the range from 36 to 44.
Polyetherdiols in the context of the present invention are diols corresponding to the general formula HOCH2xe2x80x94R6xe2x80x94CH2OH, where R6 is a hydrophobic hydrocarbon radical which may be saturated or unsaturated, linear or branched and may also contain aromatic structural elements and in which one or more CH2 units must each be replaced by an oxygen atom.
A particularly attractive class of polyetherdiols can be obtained by alkoxylation of alkanediols, such as ethane-1,2-diol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, butane-1,3-diol, pentane-1,5-diol, hexane-1,6-diol, heptane-1,7-diol and octane-1,8-diol, polyoxytetramethylenediols (polytetrahydrofurans) and dimerdiols. The production of these alkoxylated diols is normally carried out as follows: in a first step, the required diol is contacted with ethylene oxide and/or propylene oxide and the resulting mixture is reacted in the presence of an alkaline catalyst at temperatures of 20 to 200xc2x0 C. Addition products of ethylene oxide (EO) and/or propylene oxide (PO) onto the diol used are obtained in this way. The addition products are therefore EO adducts or PO adducts or EO/PO adducts with the particular diol; in the case of the EO/PO adducts, the addition of EO and PO may take place statistically or blockwise.
Polyesterdiols in the context of the invention are diols corresponding to the general formula HOCH2xe2x80x94R7xe2x80x94CH2OH, where R7 is a hydrophobic hydrocarbon radical which may be saturated or unsaturated, linear or branched and may also contain aromatic structural elements and in which one or more CH2 units must each be replaced by a COO unit. They are normally produced by reacting difunctional polyols with dicarboxylic acids or anhydrides thereof. Commonly used polyols are ethylene glycol, propane-1,2-diol, butane-1,4-diol, hexane-1,6-diol. Typical dicarboxylic acids are succinic acid, adipic acid, phthalic anhydride. Hexane-1,6-diol adipic acid polyesters are particularly preferred.
Examples of suitable aromatic compounds (c) are resorcinol, hydroquinone, 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), isomer mixtures of dihydroxydiphenyl methane (bisphenol F), tetrabromobisphenol A, 4,4xe2x80x2-dihydroxydiphenyl cyclohexane, 4,4xe2x80x2-dihydroxy-3,3-dimethyldiphenyl propane, 4,4xe2x80x2-dihydroxydiphenyl, 4,4xe2x80x2-dihydroxybenzopenol, bis-(4-hydroxyphenyl)-1,1-ethane, bis-(4-hydroxyphenyl)-1,1-isobutane, bis-(4-hydroxyphenyl)-methane, bis-(4-hydroxyphenyl(-ether, bis-(4-hydroxyphenyl)-sulfone etc. and the chlorination and bromination products of the above-mentioned compounds. Bisphenol A is most particularly preferred as compound (c). 
The epoxy compounds (d) are polyepoxides containing on average at least two epoxy groups per molecule. These epoxy compounds may be both saturated and unsaturated and aliphatic, cycloaliphatic, aromatic and heterocyclic and may also contain hydroxyl groups. They may also contain substituents which do not cause any troublesome secondary reactions under the mixing and reaction conditions, for example alkyl or aryl substituents, ether groups and the like. These epoxy compounds are preferably polyglycidyl ethers based on polyhydric, preferably dihydric alcohols, phenols, hydrogenation products of these phenols and/or novolaks (reaction products of mono- or polyhydric phenols with aldehydes, more particularly formaldehyde, in the presence of acidic catalysts). The epoxy equivalent weights of these epoxy compounds are preferably between 160 and 500 and more preferably between 170 and 250. The epoxy equivalent weight of a substance is the quantity of the substance (in grams) which contains 1 mole of oxirane rings. Preferred polyhydric phenols are the compounds described under (c). The polyglycidyl ethers of polyhydric alcohols are also suitable. Examples of such polyhydric alcohols are ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, polyoxypropylene glycols (n=1-20), 1,3-propylene glycol, 1,4-butylene glycol, pentane-1,5-diol, hexane-1,6idol, hexane-1,2,6-triol, glycerol and bis-(4-hydroxycyclohexyl)2,2-propane.
Other suitable compounds (d) are polyglycidyl ethers of polycarboxylic acids obtained by reaction of epichlorohydrin or similar epoxy compounds with an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, such as oxalic acid, succinic acid, adipic acid, glutaric acid, phthalic acid, terephthalic acid, hexahydrophthalic acid, 2,6-naphthelenedicarboxylic acid and dimerized linolenic acid. Examples are adipic acid diglycidyl ester, phthalic acid diglycidyl ester and hexahydrophthalic acid diglycidyl ester. A comprehensive list of suitable epoxy compounds (d) can be found in:
A. M. Paquin, xe2x80x9cEpoxidverbindungen und Epoxidharzexe2x80x9d, Springer-Verlag, Berlin 1958, Chapter V, pages 308 to 461 and
Lee, Neville xe2x80x9cHandbook of Epoxy Resinsxe2x80x9d 1967, Chapter 2, pages 201 and 2-33.
Mixtures of several epoxy compounds (d) may also be used,
Amines (e) suitable for the purposes of the invention are primary and/or secondary amines. Preferred amines (e) are polyamines containing at least two nitrogen atoms and at least two active aminohydrogen atoms per molecule. Aliphatic, aromatic, aliphatic-aromatic, cycloaliphatic and heterocyclic di- and polyamines may be used.
The following are examples of suitable amines (e): polyethylene amines (ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, etc.), 1,2-propylene diamine, 1,3-propylene diamine, 1,4-butane diamine, 1,5-pentane diamine, 1,3-pentane diamine, 1,6-hexane diamine, 3,3,5-trimethyl-1,6-hexanediamine, 3,5,5-trimethyl-1,6-hexane diamine, 2-methyl-1,5-pentane diamine, bis-(3-aminopropyl)-amine, N,Nxe2x80x2-bis-(3-aminopropyl)-1,2-ethane diamine, N-(3-aminopropyl)-1,2-ethane diamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, aminoethyl piperazines, the poly(alkylene oxide)diamines and triamines (such as, for example, Jeffamine D-230, Jeffamine D400, Jeffamine D-2000, Jeffamine D-4000, Jeffamine T-403, Jeffamine EDR-148, Jeffamine EDR-192, Jeffamine C-346, Jeffamine ED-600, Jeffamine ED-900, Jeffamine ED-2001), meta-xylyene diamine, phenylene diamine, 4,4xe2x80x2-diaminodiphenyl methane, toluene diamine, isophorone diamine, 3,3xe2x80x2-dimethyl4,4xe2x80x2-diaminodicyclohexyl methane, 4,4xe2x80x2-diamnodicyclohexylmethane, 2,4xe2x80x2-diaminodicyclohexyl methane, the mixture of poly(cyclohexylaromatic)amines attached by a methylene bridge (also known as MBPCM) and polyaminoamides.
Other suitable compounds (e) are the reaction products of the amines just mentioned with the above-described xcex1,xcex2-unsaturated carboxylic acid esters (a) and the reaction products of the amines just mentioned with the above-described polyepoxy compounds (d).
The present invention also relates to a process for the production of hardeners for curable epoxy resins comprising the steps of
(a) reacting one or more xcex1,xcex2-unsaturated carboxylic acid esters (I)
R2R3Cxe2x95x90CC(R4)COOR1xe2x80x83xe2x80x83(I)
where R1 is an aromatic or aliphatic radical containing up to 15 carbon atoms, the substituents R2, R3 and R4 independently of one another represent hydrogen, branched or unbranched, aliphatic or aromatic groups containing up to 20 carbon atoms or a group xe2x80x94(CH2)nxe2x80x94COOR1, where R1 is as defined above and n is a number of 0 to 10, with
(b) one or more mono-, di- or polyaminopolyalkylene oxide compounds, compounds (a) and (b) being used in such quantities that the equivalent ratio of the reactive hydrogen atoms at the aminonitrogen atoms of (b) to the Cxe2x95x90C double bond in the xcex1,xcex2-position to the group COOR1 shown in formula (I) in the carboxylic acid esters (a) is in the range from 10:1 to 1:10,
subsequently reacting the intermediate product Z1 obtained with
(c) one or more polyhydroxy compounds, the equivalent ratio of ester groups in the intermediate compound Z1 to hydroxy groups in the polyhydroxy compound (c) being adjusted to a value of 1:1.1 to 1-10,
and subsequently reacting the intermediate product Z2 obtained with
(d) one or more polyepoxides, the equivalent ratio of oxirane rings in polyepoxide (d) to hydroxyl groups in the intermediate product Z2 being adjusted to a value of 1.5:1 to 6:1,
and subsequently reacting the intermediate product Z3 obtained with
(e) one or more primary and/or secondary amines, the equivalent ratio of oxirane rings in the intermediate product Z3 to the reactive H atoms at the aminonitrogen atoms of (e) being adjusted to a value of 1:1.5to 1:20.
The present invention also relates to aqueous dispersions containing hardeners according to the invention. The content of the hardeners according to the invention in these dispersions is between 40 and 70% by weight, based on the dispersion as a whole.
The production of aqueous dispersions of the hardeners according to the invention is generally carried out as follows: the water is added to the hardeners with vigorous stirring at around 60xc2x0 C. With readily water-soluble hardeners, an aqueous solution is initially formed; with poorly water-soluble hardeners, a w/o dispersion is initially formed, ultimately changing into an o/w dispersion as more water is added.
In many cases, aqueous dispersions containing the hardeners obtainable by the process according to the invention are distinguished by very small mean particle sizes of around 500 nm or smaller. This leads to very favorable material properties of the coatings formed with these dispersions. Particularly favorable material properties are obtained when the mean particle size is below about 300 nm. The mean particle size is defined as the average of the particle sizes which is obtained by adding the values of n individual measurements and then dividing the total by n. For the purposes of the present invention, the mean particle sizes were determined using a xe2x80x9cCoulter N4 Plus Submicron Particle Sizerxe2x80x9d (manufacturer: Coulter, Miami, Fla. 33196, USA). This instrument uses the scattering of laser light at a heavily diluted dispersion for particle size determination. It performs a number of individual measurements and gives the mean particle size as the end result. The above-mentioned values relate to scattering measurements at an angle of 90xc2x0 relative to the incident laser beam.
The reactive hardeners according to the invention are suitable in combination with suitable epoxy resins and additives for the production of coatings, intermediate coatings, paints, molding compositions and curable pastes for various applications. For example, they may be used for the production of protective and/or decorative coatings on various, above all rough and porous substrates such as, for example, wood, mineral substrates (for example concrete and stone), glass, plastics (for example polyethylene, polypropylene), compost materials, ceramics and pretreated or non-pretreated metals. Their favorable properties also make the hardeners according to the invention eminently suitable for one-coat lacquering/painting. The adhering coating layer may remain unchanged as such although it may also serve as an intermediate layer, i.e. as a substrate for further coatings which in turn may consist of the same coating material or of another typical coating material. By virtue of their good dilutability and their favorable properties, the hardeners according to the invention or rather the dispersions prepared from them are also suitable for additional use in electrodeposition painting. The hardeners according to the invention may also be used for the production of water-dilutable adhesives. They may also be used as binders for textile, organic and/or inorganic materials and as an additive in plastic cements.
Accordingly, the present invention also relates to the use of the hardeners according to the invention for systems (compositions) for coating solid substrates.
Where the hardeners according to the invention are used for curing epoxy resins, other suitable hardeners (for example polymercaptans, polyisocyanates, imidazoles, polyamidoamines and any of the amines (e)) and the additives typically used in the coating industry may also be used.